Hard copy devices process images on media, typically taking the form of scanners, printers, plotters (employing inkjet or electron photography imaging technology), facsimile machines, laminating devices, and various combinations thereof, to name a few. These hardcopy devices typically transport media in a sheet form from a supply of cut sheets or a roll, to an interaction zone where scanning, printing, or post-print processing, such as laminating, overcoating or folding occurs. Often different types of media are supplied from different supply sources, such as those containing plain paper, letterhead, transparencies, pre-printed media, etc.
The relative position of the paper and the operative structures in the interaction zone is precisely maintained to effect high-quality media processing in the interaction zone. For example, in the case of an inkjet printer, printing occurs in the interaction zone and the position of an ink cartridge as it reciprocates in a back and forth motion across the media, and the positioning and control of paper as it advances past the printheads in the ink cartridge are controlled to produce high quality images. The media advancement through the hardcopy devices, and the positioning of the operators in the interaction zone are typically separately controlled, although their operation is coordinated with a hardcopy controller.
Hardcopy apparatus typically include media advancement mechanisms that serve to advance the recording media from one or more media sources through a media feed path and through the interaction zone. Again in the case of an inkjet printer, the interaction zone is typically a “printzone” where ink is applied to the paper. The media advance mechanisms move the paper through the interaction zone the desired distance, often in incremental steps, at the desired rate, and in a manner such that the media is oriented correctly relative to the devices found in the interaction zone. Achieving high quality media processing is often impeded by media feed errors such as overfeeding and underfeeding, and misalignment errors such as skewing.
Proper delivery of the media from the media supply, such as an input tray, and into the media feed path is an important first step in correctly feeding the media through the hardcopy device. In hardcopy devices that rely upon swing-arm media pick systems, recording media is held in a passive input tray. The swing-arm has a driven pick wheel that is biased onto the media and initiates movement of the media from the tray into a media feed path, which usually is curved, in the hardcopy device. To accommodate many different sizes of media, the swing-arm assembly is generally located to one side of the input tray. In operation, since swing-arm pick systems usually contact the media on one side of the sheet, the systems tend to constrain media curvature in some portions of the media, while other portions remain unconstrained. Said in another way, since the swing-arm mechanism contacts and drives the media from an off-center position, there are greater driving forces applied to some parts of the media than others. The result is often that the media twists or shifts such that the leading edge of the media arrives at the next media drive rollers at different times—a skewing error that can lead to printing errors such as poor margin control and crooked print, or media feed errors such as paper damage and jams.